chore(editor): change edgeless-text default color to black (#12361)

Closes: [BS-3506](https://linear.app/affine-design/issue/BS-3506/edgeless-text-默认改为黑色)

### Dark
<img width="691" alt="Screenshot 2025-05-19 at 19 32 52" src="https://github.com/user-attachments/assets/2927d13b-0300-4293-8f8f-7891fd87a680" />

### Light
<img width="639" alt="Screenshot 2025-05-19 at 19 33 05" src="https://github.com/user-attachments/assets/4429f6f9-b374-4b17-87f4-ae09204f1538" />

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->

## Summary by CodeRabbit

- **New Features**
  - Improved edgeless text block styling to support theme-based color, font, and alignment settings.

- **Style**
  - Updated the default text color in edgeless text blocks to black, with support for separate dark and light mode colors.

- **Bug Fixes**
  - Ensured the color picker and block rendering reflect the updated default color.

- **Tests**
  - Adjusted tests and snapshots to expect the new default color and theme-based color structure.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/model/src/themes/default.ts

@@ -115,7 +115,7 @@ export const DefaultTheme: Theme = {
   black: Black,
   white: White,
   transparent: Transparent,
-  textColor: Medium.Blue,
+  textColor: Black,
   shapeTextColor: pureBlack,
   shapeStrokeColor: Medium.Yellow,
   shapeFillColor: Medium.Yellow,